Temperature dependence of magnetic domains in magnetite crystals

Synthetically grown and natural multidomain magnetite crystals (d ≥ 30 µm) have strongly temperature‐dependent magnetic domain structures. The unblocking of domain walls at moderate temperatures (T < 120°C) makes these magnetite grains unsuitable as paleomagnetic recorders. Approximately 15% of the smaller hydrothermally grown magnetite crystals (d ≤ 10 µm) show stable domain patterns when heated to 350°C. These magnetites with temperature‐independent domain structures can possibly account for paleo‐magnetic remanences with high blocking temperatures.